1. Field of the Invention
The present invention relates to a rotational angle measuring apparatus used in detecting a steering angle of a steering of a vehicle or the like.
2. Description of the Related Art
As a rotational angle measuring apparatus, there is provided, for example, an apparatus of detecting a steering angle of a steering for automatic control for controlling an irradiating direction of a headlamp variably to the left and to the right in cooperation with a steering wheel in a vehicle or the like. In detecting such a steering angle, the steering wheel is rotated by several turns respectively to the left and to the right and therefore, it is requested that a rotational angle of a steering shaft exceeding 360 degrees can be measured.
As such a steering angle detecting apparatus, there is provided a constitution disclosed in Japanese Patent Laid-Open No. 287608/1999.
According to the apparatus, a slit is provided at a light blocking plate fixed to a steering shaft, a relative rotational angle of the light blocking plate is detected by a photointerruptor in which a light emitting element and a light receiving element are opposed to each other, a resistance value of a variable resistor is changed by an intermittently driven gear set rotated intermittently for respective single turn of the steering shaft, a number of turns (frequencies) by a unit of 360 degrees is detected and an operation is executed by combining detected results of these to thereby calculate a steering angle constituting an absolute rotational angle.
According to the steering angle detecting apparatus, for example, when an ignition switch is made OFF and thereafter the ignition switch is made ON again, the number of turns of the steering shaft is immediately known by the resistance value of the variable resistor and therefore, when the relative rotational angle is found, the absolute rotational angle is also provided easily.
However, according to the above-described steering angle detecting apparatus, a number of parts is large and therefore, there poses a problem that cost is increased and the mountability is poor in a narrow space around the steering shaft.
Hence, as other steering angle detecting apparatus reducing a number of parts, there is provided a constitution disclosed in Japanese Patent Laid-Open No. 88065/2000.
According to the apparatus, there is used a photointerruptor comprising a reference position sensor and two of relative position sensors with regard to a light blocking plate and by tracking signals of these and subjecting the signals to an operational processing by CPU, a steering angle exceeding 360 degrees is detected while dispensing with a variable resistor driven by an intermittently driven gear set or the like.
In this case, the signal of the photointerruptor needs to monitor always, when data of the steering angle is not used as in the case in which the ignition switch is made OFF, in order to restrain power consumption of a battery, there is brought about a sleep state in which one of the relative position sensors is left and power supply to other of the sensors is made OFF. Further, when rotation of the steering shaft is detected by an operating one of the relative position sensors, the sleep state is released.
Power is supplied intermittently to the operating one of the relative position sensors.
However, in order to detect a small amount of rotational movement of the steering shaft, there is selected the relative position sensor operated in the sleep state with respect to the densest slits among slits formed at the light blocking plate. Therefore, in order to avoid a failure in detecting a number of slits passing through the relative position sensor in accordance with steering speed, an interval of power supply to the relative position sensor needs to be extremely short in correspondence with an interval between slits and there poses a problem that current consumption is not reduced as aimed.
Meanwhile, in a vehicle, large current is consumed in cranking in starting an engine and there poses a problem that voltage of the battery is lowered and therefore, a capacitor having a large capacitance needs to be provided at a power source portion of the steering angle detecting apparatus in order to maintain stable operation of an inner circuit of the steering angle detecting apparatus and therefore, large-sized formation and high cost of the apparatus are unavoidable.
Further, in the case in which a period at an order of turns is not detected directly but detected by tracking the signal of the relative position sensor indicating an angular position in the period, when the steering shaft is rotated by one turn or more after removing the battery of the vehicle constituting the power source, erroneous data is constituted even when the frequency is preserved in a memory and therefore, initial setting needs to carry out again.
Therefore, in view of the above-described problems of the related art, it is an object of the invention to provide a rotational angle measuring apparatus capable of remarkably reducing power consumption at a pose in which detected data is not used, realized by a simple constitution, dispensing with reexecution of initial setting and suitable for detecting a steering angle of a steering.
Hence, according to a first aspect of the invention, there is provided a rotational angle measuring apparatus comprising a rotating member rotated in cooperation with a rotating body constituting an object of measurement, an angle sensor attached to the rotating member for detecting a periodic angular position thereof, an involatile data storing portion for storing a reference position of the angle sensor, and operating and controlling means for subjecting the reference position and detected data from the angle sensor to an operational processing to thereby calculate a frequency of the rotating body constituting the object of measurement and calculating an absolute rotational angle of the rotating body constituting the object of measurement to thereby constitute a measured output, wherein the operating and controlling means switches a mode thereof from a normal operation mode for continuously reading the detected data from the angle sensor and executing the operational processing to a low current consumption mode for executing the operational processing by reading the detected data from the angle sensor by an intermittent operation by receiving a pause signal from outside.
The reference position of the angle sensor is stored to the involatile data storing portion and therefore, while constructing the angle sensor by a simple constitution of detecting a periodic angular position, initial setting needs not to execute again after detaching or attaching a power source.
In the intermittent operation of the operating and controlling means in the low current consumption mode, an interval of the intermittent operation may be to the degree of tracking a change in a frequency and therefore, current consumption is remarkably reduced.
According to a second aspect of the invention, particularly, a plurality of angle sensors are constituted and the operating and controlling means constitutes a measured output by an average value of absolute rotational angles based on the respective angle sensors.
According to a third aspect of the invention, the operating and controlling means determines that an abnormality is caused when a difference between the absolute rotational angles based on the angular positions detected by the detective angle sensors is larger than a predetermined values.
According to a fourth aspect of the invention, in the operating and controlling means, when there is present an absolute rotational angle in which a difference between the absolute rotational angle and an average value of absolute rotational angles based on the angular positions detected by the respective angle sensors, is larger than a predetermined value, the measured output is constituted by an average value of other absolute rotational angles by excluding the absolute rotational angle.
The absolute rotational angle having a large difference from the average value is excluded as abnormal and therefore, accuracy of the measured output is promoted.
According to a fifth aspect of the invention, the rotating body constituting the object of measurement is a steering shaft, the measured output is a steering angle and the pause signal is a signal for making an ignition switch off.
The low current consumption mode is constituted when the ignition switch is made off, which does not need the measured output of the steering angle and therefore, power consumption of a vehicle-mounted battery is reduced.
According to a sixth aspect of the invention, the operating and controlling means sets a frequency to null by an angular position when the vehicle is determined to be brought into a linearly advancing state based on a signal from a sensor for detecting a behavior of the vehicle when a power source has been removed and thereafter connected again.
Even when the steering shaft is rotated during a time period in which the power source is removed, the frequency is automatically set to null correctly when the vehicle is brought into the linearly advancing state.
According to a seventh aspect of the invention, the rotating body constituting the object of measurement is the steering shaft of the vehicle and particularly in the third aspect of the invention, when the operating and controlling means determines that an abnormality is caused, a range of the steering angle is calculated based on a signal from a sensor for detecting a behavior of the vehicle and the steering angle is outputted as the measured output based on an absolute rotational angle produced by excluding an absolute rotational angle deviated from the range of the steering angle.
The absolute rotational angle deviated from the range of the steering angle is excluded and therefore, accuracy of the steering angle is promoted.
According to an eighth aspect of the invention, in the low current consumption mode, a power source is supplied to the angle sensor only in an intermittent operation of the operating and controlling means.
In addition to a reduction in current consumption of the operating and controlling means per se, power consumption by the angle sensor is also reduced.
According to a ninth aspect of the invention, the operating and controlling means monitors a voltage of the power source and constitutes the low current consumption mode when the voltage becomes lower than a predetermined voltage.
By reducing power consumption in low voltage, operation of the operating and controlling means and the like are prevented from being unstable.